linux-kernel - Re: [PATCH] Disable -Wframe-larger-than warnings with KASAN=y

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Date:	Fri, 16 Oct 2015 20:19:43 +0300
From:	Andrey Ryabinin <ryabinin.a.a@...il.com>
To:	Andi Kleen <ak@...ux.intel.com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Kozlov Sergey <serjk@...up.ru>, kbuild-all@...org,
	linux-media@...r.kernel.org, Abylay Ospan <aospan@...up.ru>
Subject: Re: [PATCH] Disable -Wframe-larger-than warnings with KASAN=y



16 октября 2015 г. 19:47:00 GMT+03:00, Andi Kleen <ak@...ux.intel.com> пишет:
>On Fri, Oct 16, 2015 at 07:02:10PM +0300, Andrey Ryabinin wrote:
>> When the kernel compiled with KASAN=y, GCC adds redzones
>> for each variable on stack. This enlarges function's stack
>> frame and causes:
>> 	'warning: the frame size of X bytes is larger than Y bytes'
>> 
>> The worst case I've seen for now is following:
>>  ../net/wireless/nl80211.c: In function ‘nl80211_send_wiphy’:
>>  ../net/wireless/nl80211.c:1731:1: warning: the frame size of 5448
>bytes is larger than 2048 bytes [-Wframe-larger-than=]
>>   }
>>    ^
>> That kind of warning becomes useless with KASAN=y. It doesn't
>necessarily
>> indicate that there is some problem in the code, thus we should turn
>it off.
>
>If KASAN is really bloating the stack that much you may need to
>consider
>increasing the stack size with KASAN on. We have 16K now, but even that
>may not be enough if you more than double it.
>

Such huge bloat only in a few places, anyway it's done already. Stack is 32k with kasan.

>Otherwise it may just crash with KASAN on in more complex setups.
>
>-Andi
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